The present invention relates to a method for monitoring the condition of a shoe roll, where the method is used for analyzing continuously the lubricant used in the lubrication system integrated with a shoe roll, and where the analysis determines the amount of contaminant particles which have entered the lubricant. The present invention also relates to a corresponding device.
Shoe rolls are especially used in web forming machines as press rolls and in shoe calenders. The specific feature of a shoe roll is a thin and flexible belt of a belt roll, which is guided into a curved nip formed by a counter roll and a load shoe, also referred to as a long nip. The belt of a belt roll usually has a core structure woven of reinforcement fibers, and one or more cast layers of polyurethane on each side of the core structure. In addition to polyurethane, polyamide and/or polyester can also be used in the core structure. A belt has good endurance in normal use. Especially the wear resistance of the belt is good also in long-term use.
In practice, the belt of a belt roll is placed around a shoe roll and fastened to revolving end pieces so that an enclosed structure is formed. It is hence impossible to determine the condition of the inside of the belt of a belt roll. Even though there is a layer of lubricant between the belt and the load shoe, the inner surface of the belt wears, too. Especially local damage can be extensive, which may lead to the breakage of the belt during operation. However, the only way to determine the condition of a belt is to remove the belt from the shoe roll. Another option is to use an endoscope through a connection. Both of these methods require a standstill of several hours. Moreover, the belt may break when it is removed, and an endoscope can only examine a small limited area on the belt. In other words, monitoring the condition of the shoe roll and especially the condition of its belt is a major problem, and if the belt breaks surprisingly, the resulting costs are high.
The lubricant is usually oil, and there are various types of devices for monitoring its properties. The said devices can be used for determining the need for oil change, but this does not indicate the condition of the belt of a belt roll. In addition to the ageing of oil, the devices can also be used for detecting microparticles which are contaminants in the oil. It is hence possible to detect, for example, small metal particles which come off the bearings of the shoe roll, and this can be used as a basis for making conclusions of the condition of the machine component in question. However, the condition of the belt of a belt roll is still not ascertained.